Schools spending is about £40bil, defence £48bil and NHS £190bil
The cost of the Royal family wouldn't make any noticeable difference to budgets of that scale (it's less than the permitted margins for rounding in the accounts)
What I've not been able to find out is what the Prime Minister costs, not just his salary (published) but the total for staff (inc employers NICs, superannuation etc) and the two official residences (upkeep, utilities, gardening - and wallpaper), travel, security, official entertainment, other expenses